1. Field of the Invention
The invention relates in general to a method for selecting and adjusting scanner illuminants, and more particularly to a scanner illuminant selecting and adjusting method in accordance with the types of power supply.
2. Description of the Related Art
Of all the personal computer peripherals, scanner can be said to be one of the essential peripherals. As for the scanners currently available in the market, types of power supply are adopted: one adopts self power and is connected to an urban power 340 (as shown in FIG. 3), and the other adopts bus power and is connected to a computer host 350 (as shown in FIG. 3).
Since the self power provides the scanner with higher power, the illuminant device installed in a self-powered scanner is allowed to be more power consuming. Under this circumstance, a cold cathode fluorescent lamp (CCFL) is normally used as the illuminant device. The cold cathode fluorescent lamp, although has the advantage of producing a higher level of brightness, is disadvantaged by being more power consuming and inconvenient to use.
Normally, the bus-powered scanner is convenient to use for its power is directly supplied by the computer. Due to the fact that the power supplied by bus power is relatively low, a light emitting diode (LED), which has the advantage of power saving, is normally installed as the illuminant device. The bus-powered scanner has the advantage of power saving, but produces a lower level of brightness when scanning images.
It is understood from the above disclosures that a conventional scanner has the following disadvantages:
1. More purchase costs. Scanners powered by self power and scanners powered by bus power have their individual applicable situations. To assure that different situations are all covered, two scanners covering different types of power supply are needed. Therefore more costs will be expended.
2. Inconvenience of use. While there are situations when quality and speed of image scanning carries more weight than power saving and convenience of use, there are situations when power saving and convenience of use are more important than quality and speed of image scanning. Since different situations require different scanners adopting different types of power supply, inconvenience of use arises.